GPCRs are a family of cell surface proteins involved in mediating many of the biological actions of neurotransmitters in the brain. They play a critical role in CNS physiology and are a major target for drug discovery in the pharmaceutical industry. The majority of GPCRs in the brain are orphans, with no known ligand or function. Orphan GPCRs (oGPCR) may provide major opportunities in the development of new drugs to better treat common and pervasive mental disorders. A major problem in discovering drugs targeting these receptors is the lack of appropriate technologies for compound library screening. We propose in this grant to develop a technology that will allow for discovery of drugs against oGPCRs. This grant will be a joint effort between three biotechnology companies focused on GPCR drug discovery. Scientists at Patobios have discovered that inserting an NLS in the proximal C-terminal region of GPCRs causes the receptor to translocate from the cell surface membrane to the cytosol. When a ligand binds to the GPCR with the NLS, it causes the receptor to be retained at the cell surface preventing translocation providing a readout of binding of high affinity ligands to the GPCR independent of the receptors function. DiscoveRx has developed an enzyme fragment complementation (EFC) technology that can be used to detect surface expression of GPCRs in a HTS format. In this grant we will merge these technologies to develop a HTS screening assay to identify the binding of ligands to oGPCRs. The third company, Nura has employed gene ko technologies to identify three oGPCRs with phenotypes that suggest they may have roles in mental disorders. We will adapt the Patobios/DiscoveRx HTS technologies to these orphans so that in future studies we will employ the drug discovery capabilities of Nura to identify high affinity ligands targeting these receptors. This will serve two purposes; 1) it will validate the utility of the ligand screening assay for GPCR drug discovery and; 2) it may lead to the development of novel drugs targeting these receptors to treat mental disorders. This project will develop a novel technology that will allow for the discovery of unique drugs targeting orphan G protein linked receptors. At present, there is no comparable technology that will allow for drug screening against this large family of receptors. Drug discovered and developed against these receptors could have the potential for treating a number of mental disorders including anxiety and obesity. [unreadable] [unreadable] [unreadable]